1. Field of the Invention
This invention relates to a system for adding or removing fluid from storage, and in particular to an adjustable pick up device for removing fuel from a fuel storage tank.
2. Description of the Related Art
Many problems exist when storing fuel. Fuel is an organic compound that reacts with air, water and microbiological growth. It has a relatively short shelf life and will degrade over time. Thus when fuel is stored, contaminants are formed that settle out into the fuel. The heaviest contaminants fall to the bottom of the storage tank, while lighter particles remain suspended in layers in the fuel. As a result of this stratification, less contaminated fuel remains higher in the column.
In order to maximize the usable volume of a storage tank, fuel pick up tubes are often placed within a few inches of the bottom of the tank. Having the pick up tube near the bottom allows more fuel to be withdrawn before the need to refill the tank. This can be critical, especially for emergency power systems that may have to run for long periods of time without being refueled. Yet, such a design places the pick up tube in the most contaminated area of the stored fuel.
Other storage tank features contribute to fuel contamination problems. Some storage tanks are vented to the atmosphere to relieve pressure build up. Yet, such venting introduces moisture and airborne microorganisms into the tank, which eventually make their way to the bottom of the tank due to condensation and gravity. The microorganisms grow and reproduce in this environment, living in the water while feeding on the fuel. Over time, an interface layer, that can be made up of a stringy, black mass of sediments, will form between the fuel and the water. Additional sediments also form on the tank bottom as byproducts of the microorganisms' biological processes. As a result, the pH of accumulated water drops providing a corrosive environment. If left unchecked, layers of water and sludge accumulate from the bottom, and upward toward the middle of the storage tank.
Many storage tanks also have a return fuel line through which unused fuel is discharged back into the tank. The problem of suspended sludge accumulating near the bottom of the tank is compounded when diesel engines dump fuel back into the tank through this line.
Today's expensive fuel equipment has little tolerance for such dirty, contaminated fuel. For example, the orifices on injectors are smaller to make engines more fuel efficient. Consequently, the potential for injection wear is greater when fuel is delivered from a contaminated source. Moreover, due to the present practice of introducing chemicals to the fuel through the cracking process (to increase yield), current fuel types are more dynamic, and will precipitate particles that link together to form additional sludge. The National Fire Protection Association recognizes the potential for problems associated with contaminated fuel and has provided a Standard that “fuel system design shall provide for a supply of clean fuel to the prime mover.” NFPA Standard 110, 7.9.1.2.
Various attempts have been made for reducing the previously identified problems associated with stored fuel. Fuel storage tanks are typically inspected and periodically cleaned to remove the build up of contaminants. In addition, biocides or biostats can be added to the tank to destroy or inhibit the growth of microorganisms. Finally, filters can be installed and periodically changed. Because of budget constraints and differing maintenance philosophies, however, such measures are not always taken. What is needed is a fuel pick up device that will remove fuel from the cleanest part of the tank while maximizing the usable volume of a storage tank. It is to such a device that the present invention is primarily directed.